Decomposition: When can it occur, and what are some signs of it happening.
Sample heated too much in air
Darkening or effervescence of the sample
What are Polymorphs?
Different crystalline forms of the same compound which have different but sharp melting points.
What are Hydrates?
Compounds that cystallize with water incorporated in their crystal latice in a definite proportion by weight.
Hydrates melt at a different temp than the anhydrous compound.
What is a racemic mixture or racemate?
A pair of enantiomers. The enantiomers have identical melting points, but together as a racemic mixture they do not melt at that temperature and show characteristics of an impure compound.
The minimum melting point of a mixture.
-distill at a constant boiling point
-behave as a single pure compound
To use boiling point...
pressure must remain constant.
The ideal recrystallization solvent is one that at least meets the following criteria
- Does not react with the compound to be purified
-Dissolves a moderately large amount of compound when "boiling" hot
-Dissolves a small amount of compound when at room temp.
-Is able to remove impurities. Impurities should either be highly soluble or highly insoluble.
The ratio of solubilities is known as
-Partition coefficient K
dissolving NaCl in the water layer to increase the distribution coefficient of an organic compound in the organic solvent.